Other than weight, which is obvious, what are the pros and cons of an aluminum hemi block versus an iron hemi block for a street/strip style car? Thanks, Joel

Ring seal is much better with an iron block, hence Pro Stock still using them.
I know you said for street use but my thinking is that the iron blocks will seal up better than aluminum block with steel sleeves will when being driven at normal running coolant temps.

For all the naysayers saying all or most of the new cars come with aluminum blocks look at the new Challengers with the Hi Po motors using iron blocks instead of aluminum.
The new cars blocks were designed for that application, the aftermarket replacement blocks for early American muscle car motors weren't designed to be better than the original iron blocks were.

This ^

General consensus is 3 - 4 % more power in favour of the iron block (upto 40 hp @ 1000hp) due to ring sealing, you will also lose more if you are using some sort of boost. With more modern aluminium blocks it's reputed to be less though. Whats worth more, 30 hp (@ 750hp) or the 150lb weight saving ?
You also have to look at availability, how many iron Mopar blocks are available with a 4.84 bore spacing ?

A Keith Black block is sexier than an iron block and only adds $2,000 to the total build price. I like sexy.

I already have the early Mopar performance mega block iron block sitting here all machined, all it needs is a final hone. Everything is squared up, bore sitting at 4.495, lifter bores bushed. I have some good stage 5 heads that flow 480/300 all ready to go, and a Velasco 4.5 in crank. Mostly I just need rods, pistons, and a cam. So the question is should follow my own advice that I give other people of not using something just because you have it, but use what's best for the situation? And I'm working on trying to figure out what is best for the situation? Hence this question. I emailed Tim banning a week ago to find out what's the availability on the KB blocks and what machining operations have to be done before assembly but I haven't heard back from him yet.
This would be for a naturally aspirated drag week motor.

True, but some counterpoint examples - 13/14 GT500's have an aluminum block, unsleeved, with a plasma bore coating. The newer GT500's have conventional aluminum blocks with sleeves. They are good for 1200+ hp. Lots of LS's making above that as well. It can be done.

Agree the ring seal is a little better on alumimum vs. cast iron, but like Tig said- what's going to help the car more overall? Losing 30 hp from not quite as good ring seal, or losing 150 pounds off the nose of the car? Bench racing, at 2800 pounds and 850-820 hp, the weight savings with 30 less hp would be 0.05 quicker than more power with an iron block.

The early M/P mega blocks are thought to be lighter than the later ones. I know we only saved around 70lb when we swapped from a iron block 528 to a KB block 572, many years ago. Used the same top end, the crank and rods would have been heavier on the 572 but I remember expecting a lot more weight savings at the time.

I have had a lot of trouble with the aluminum blocks. I prefer the cast iron ones. Bores can be held tighter, and rounder......Feels like its making more hp, but its heavier.

Besides the sleeves leaking coolant every where,. I think in some of the aluminum blocks there is not enough material behind the sleeves to keep it round during boring and honing. I think if your going to go aluminum, you want nice thick sleeves, and you want nice support behind it. Keep the bores smaller, and put your own sleeves in....

If the cost isn't a deal breaker and there is no rule against using it, I've never heard of any reasons to not give it a try.

The lighter weight should noticeably improve the car overall....even normal street driving and braking should be better.

I debated this very issue on my last 540 inch street Hemi build. I have mostly had iron blocks, but have had 1 aluminum Hemi block that was in a Dart and have helped buddies with their aluminum engines.

I went with the iron this time for two simple reasons: First, I have had a few issues getting aluminum to seal. Never had those problems with any iron blocks. Second, I sometimes jump on it before it is fully warmed up. Not a real issue with iron, but could be in certain circumstances with aluminum. For a less experienced builder like myself, the iron was just less likely to cause me an issue.

Then there's the fact that 150lbs or so on the nose is not a big issue for my application.

You guys with more building experience and different uses may not have those issues. But they could have been for me.

I just weighed my iron mega block. 266 lb. Tim banning said in an email that the KB block weighs approximately 180 lb. So that is an 86 lb saving. Still very significant, but not as dramatic as what has been assumed.

I have a new 4.995" KB and weighed it and it was 162 lbs.

Almost every car that races in the F/X (9.75 and quicker) N/SS or Hemi classes run aluminum blocks. There aren't many that have been 9.0 at my weight. With the exception of Caseys B-1 all are lighter than mine. Granted not everybody's combo is the same. But in my mind $7-$8 K for an aluminum block could be used to a better advantage elsewhere. Especialy when you already own an iron block. My Mega Bock weighs 277lbs.
Doug

I talked to Total Seal a while back about aluminum blocks.

They said you can seal one up but it is very difficult.

They did not go into the details.

Joel, all I can tell you is that I've been very happy w/ my KB aluminum hemi block. Been running it since 2006. Ball honed it a couple of times during freshen ups and it ran great every time. Didn't put "fresh" bores in it until 2019 when I hurt 3 pistons due to a nitrous mishap.
Comparing to some other similar combos, I don't think mine is really missing any power.
I think the weight loss is worth whatever small amount of power is lost from ring seal. If you don't need the extra weight up front, I'd go aluminum. Unless you completely destroy it, it can be easily repaired.
Now, I think my car could benefit from an iron block simply for the weight up front to help keep the front down.

The lash will open up more as it warms. But for a street combo, where tractoon is poor, the extra weight off the front end is golden. You can't recover that with the extra power of iron. Every last ounce of weight moved aft will help. I really noticed this when i changed weight distribution on my race car. I have enough driveway to do a test hit, and moving weight forward for the track absolutely killed traction on a non prepped surface, despite 15x33 slicks.